There are two issues when upgrading to version 1.2.14 when using a postgresql database. All these errors occur in admin/install.php

First the system prevents you from having an empty hostname, which is what you need when connecting via unix sockets and it gives you an incorrect error message:
"database connection settings do not exist?"
(probably this check is made more than once in different places)

Second, the connection fails, because you need to supply the database name in line 302: $t_result = @$g_db->Connect( $f_hostname, $f_admin_username, $f_admin_password )
(as fourth parameter)
This error probably also occurs somewhere else in admin/install.php
(e.g. installation)
The (incorrect) error message here is: "Does administrative user have access to the database?"